The aim of this study is to understand more completely the behavioral mechanisms that regulate animal social organization. The proposed research will address the following problems related to this aim: (1) the behavioral regulation and ecological consequences of deferred reproduction among males of polygynous species; (2) behavioral mechanisms underlying variations in territorial behavior; and (3) behavioral processes in the formation of heterosexual bonds. Four related species of blackbirds and grackles (Agelaius icterocephalus, A. phoeniceus, Quiscalus major, Q. quiscula) have been chosen to allow comparisons of monogamous and polygynous mating systems and variations in territorial behavior. The study will have three parts, corresponding to the problems just enumerated. (1) To assess the importance of social interactions in the development of male reproductive behavior in monogamous and polygynous species, I propose to compare quantitatively the behavior of young male Agelaius caged with and without older males. (2) Field experiments planned especially for A. icterocephalus will explore situations that influence territorial males' agonistic responses and movements as functions of location. (3) The heterosexual interactions of each species will be examined for reciprocal interactions between mates and the establishment of a characteristic distance between mates through approach/avoidance responses.